X-ray fluorescence (XRF) measurement, and specifically X-ray microfluorescence (i.e., X-ray fluorescence using narrow, focused excitation beams), is gaining increasing attention as a method for testing semiconductor wafers. XRF itself is a well-known technique for determining the elemental composition of a sample. XRF analyzers generally include an X-ray source, which irradiates the sample, and an X-ray detector, for detecting the X-ray fluorescence emitted by the sample in response to the irradiation. Each element in the sample emits X-ray fluorescence in energy bands that are characteristic of the element. The detected X-ray fluorescence is analyzed to find the energies or, equivalently, the wavelengths of the detected photons, and the qualitative and/or quantitative composition of the sample is determined based on this analysis.
U.S. Pat. No. 6,108,398, for example, whose disclosure is incorporated herein by reference, describes an XRF analyzer and a method for analyzing a sample. The analyzer includes an X-ray beam generator, which generates an X-ray beam incident at a spot on the sample and creates a plurality of fluorescent X-ray photons. An array of semiconductor detectors is arranged around the spot so as to capture the fluorescent X-ray photons. The analyzer produces electrical pulses suitable for analysis of the sample.
Small-angle X-ray scattering (SAXS) is another X-ray based method, which may be used for surface layer characterization. It is described, for example, by Parrill et al., in “GISAXS—Glancing Incidence Small Angle X-ray Scattering,” Journal de Physique IV 3 (December, 1993), pages 411-417, which is incorporated herein by reference. In this method, an incident X-ray beam is totally externally reflected from a surface. The evanescent wave within the surface region is scattered by microscopic structures within the region. Measurement of the scattered evanescent wave can provide information about these structures. For example, Parrill et al. describe the use of this technique for determining size information regarding islands associated with film growth on the surface.
SAXS may be combined with X-ray reflectometry (XRR) measurements, as described, for example, in U.S. Pat. No. 6,895,075, whose disclosure is incorporated herein by reference. In the embodiments disclosed in this patent, X-ray inspection apparatus comprises a radiation source, which is configured to irradiate a small area on a surface of a sample. The X-ray optics control the radiation beam so as to adjust the angular width and height of the beam appropriately for XRR or SAXS. An array of detector elements is positioned to detect radiation that is scattered from the irradiated area as a function of azimuth for SAXS or of elevation angle for XRR.
Techniques have been developed recently for depositing nano-particles on a substrate. In the context of the present patent application and in the claims, the term “nano-particle” refers to particles whose dimensions are normally measured in nanometers, i.e., particles having a dimension between 1 nm and 999 nm. For example, U.S. Pat. No. 7,071,007 describes a method of forming a low-voltage drive thin film ferroelectric capacitor, which includes a nanocomposite layer including nano-particles of platinum. The nanocomposite structure and particle sizes are observed using a transmission electron microscope (TEM).